Vibration harvesters typically are linear mass-spring devices working at resonance. A different approach is here proposed based on nonlinear converters that exploit stochastic resonance with white-noise excitation.\ud It consists of a piezoelectric beam converter coupled to permanent magnets to create a bistable system. Under proper conditions, the system bounces between two stable states in response to random excitation, which significantly improves energy harvesting from wide-spectrum vibrations. The background theory is discussed based on a simplified monodimensional model which includes nonlinearity.\ud A cantilever beam with added nonlinearity was simulated by using a MATLAB® Stochastic Differential Equation (SDE) Toolbox demonstrating the expected improvement under white-noise vibrations. Nonlinear converters were then realized by screen printing low-curing-temperature lead zirconate titanate (PZT) films on steel cantilevers equipped with magnets. Experimental tests were performed by measuring both the beam deflection and the output voltage under excitation by random vibrations at varying degree of nonlinearity added to the system. The obtained results show that the performances of the converter in terms of output voltage at parity of mechanical excitation are markedly improved when the system is made bistable. Furthermore, the principle was also preliminarily validated on aMEMSU-shaped cantilever beam that was purposely designed and fabricated in SOI technology. This demonstrates the possibility to downscale the principle here proposed in the perspective of a MEMS harvester based on nonlinear piezoelectric converters

This paper reports a novel bistable microelectromechanical system for energy harvesting applications. In particular, we focus here on methodologies and devices for recovering energy from mechanical vibrations. A common energy harvesting approach is based on vibrating mechanical bodies that collect energy through the adoption of self-generating materials. This family of systems has a linear mass-spring damping behaviour and shows good performance around its natural frequency. However, it is not generally suitable for energy recovery in a wide spectrum of frequencies as expected in the vast majority of cases when ambient vibrations assume different forms and the energy is distributed over a wide range of frequencies. Furthermore, whenever the vibrations have a low frequency content the implementation of an integrated energy harvesting device is challenging; in fact large masses and devices would be needed to obtain resonances at low frequencies. Here, the idea is to consider the nonlinear behaviour of a bistable system to enhance device performances in terms of response to external vibrations. The switching mechanism is based on a structure that oscillates around one of the two stable states when the stimulus is not large enough to switch to the other stable state and that moves around the other stable state as soon as it is excited over the threshold. A response improvement can be demonstrated compared to the classical linear approach. Indeed, both a wider spectrum will appear as a consequence of the nonlinear term and a significant amount of energy is collected at low frequencies. In this paper the bistable working principle is first described and analytically modelled, and then a numerical study based on stochastic differential equations (SDE) is realized to evaluate the behaviour of a MEMS device. A micromachined SOI prototype has been realized and a measurement campaign validated the nonlinear mechanism. As expected, the study shows that the nonlinear system exhibits a low pass filter behaviour suitable for harvesting ambient energy at low frequency.

Vibration harvesters typically are linear mass-spring devices working at resonance. A different approach is here proposed based on nonlinear converters that exploit stochastic resonance with white-noise excitation. A piezoelectric beam converter is coupled to permanent magnets creating a bistable system bouncing between two stable states in response to random excitation. Under proper conditions, this significantly improves energy harvesting from wide-spectrum vibrations. A cantilever beam with added nonlinearity has been simulated by using a MATLAB ® Stochastic Differential Equation (SDE) Toolbox with a white-noise vibration. A nonlinear converter was then realized by screen printing low-curing-temperature lead zirconate titanate (PZT) films on steel cantilevers and excited with white-noise vibrations. Experimental results show that the performances of the converter in terms of output voltage at parity of mechanical excitation are markedly improved.

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The continuous development of internet of things (IoT) infrastructure and applications is paving the way for advanced and innovative ideas and solutions, some of which are pushing the limits of state-of-the-art technology. The increasing demand for Wireless Sensor Nodes (WSNs) able to collect and transmit data through wireless communication channels, while often positioned in locations that are difficult to access, is driving research into innovative solutions involving energy harvesting (EH) and wireless power transfer (WPT) to eventually allow battery-free sensor nodes. Due to the pervasiveness of radio frequency (RF) energy, RF EH and WPT are key technologies with the potential to power IoT devices and smart sensing architectures involving nodes that need to be wireless, maintenance free, and sufficiently low in cost to promote their use almost anywhere. This paper presents a state-of-the-art, ultra-low power 2.5 μ W highly integrated mixed signal system on chip (SoC), for multi-source energy harvesting and wireless power transfer. It introduces a novel architecture that integrates an ultra-low power intelligent power management, an RF to DC converter with very low power sensitivity and high power conversion efficiency (PCE), an Amplitude-Shift-Keying/Frequency-Shift-Keying (ASK/FSK) receiver and digital circuitry to achieve the advantage to cope, in a versatile way and with minimal use of external components, with the wide variety of energy sources and use cases. Diverse methods for powering Wireless Sensor Nodes through energy harvesting and wireless power transfer are implemented providing related system architectures and experimental results.